Method of producing ferro-nickel or metallic nickel

ABSTRACT

A method of refining nickel from iron-rich nickel ore by adding silica therein, so that the silica may form fayalite with iron in the ore for suppressing the reduction of iron by taking advantage of the very low reducibility of fayalite. Silica to be added to the iron-rich nickel ore can be prepared by separating magnesia from nickel magnesium silicate ore, while using the exhaust gas from the nickel refining process as the source of carbon dioxide gas required for the magnesia separation. In this case, magnesia becomes a by-product of the nickel refining process.

United States Patent [1 1 Sato et a1.

[ METHOD OF PRODUCING FERRO-NICKEL OR METALLIC NICKEL [75] Inventors: Yohta Sato, Tokyo; Masakata Matsuda, Miyazu; Yukio Ohi, Miyazu; Toyomi Matsumori, Miyazu, all of Japan [73] Assignee: Nippon Yakin Kogyo Company Limited, Tokyo, Japan [22] Filed: May 26, 1970 [21] App]. No.: 40,545

[30] Foreign Application Priority Data Feb. 2, 1970 Japan 45/8428 Feb. 9, 1970 Japan 45/10906 [52] U.S. C] 75/82, 75/123, 423/142,

[51] Int. Cl. C22b 23/06, C22c 37/00, COlf 5/06 [58] Field of Search 75/82, 31, 123, 128; 23/67; 423/142, 158, 160, 637

' [56] References Cited UNITED STATES PATENTS 697,370 4/1902 Shuler 75/82 X 1 Oct. 16, 1973 Primary Examiner-Edward J. Meros Assistant Examiner-Hoke S. Miller Attorney-Fleit, Gipple and Jacobson [5 7] ABSTRACT A method of refining nickel from iron-rich nickel ore by adding silica therein, so that the silica may form fayalite with iron in the ore for suppressing the reduction of iron by taking advantage of the very low reducibility of fayalite. Silica to be added to the iron-rich nickel ore can be prepared by separating magnesia from nickel magnesium silicate ore, while using the exhaust gas from the nickel refining process as the source of carbon dioxide gas required for the magnesia separation. In this case, magnesia becomes a byproduct of the nickel refining process.

8 Claims, 10 Drawing Figures Iron rich Lnickel ore L Resldue l Heating for reduction Magnetic seoronon I I Ferro-nickel of s metallic nickel Filtrote Magnesia PAiENlEDnm i6 I975 3.765.873

SHEEI 01 ill 10 Nickel magnesium Silcatei are Cru shing I" 1 i l l Calcination Water i Slurry I CO2 treatment l i g ggl 252 Residue Filtrate Magnesia Mixing l Heating for redutition Luppe Crushing i Magnetic separation Ferro-nickel or Slug metallic nickel INVENTCRS YoHa 531m Ndsakaia NaksuJa Tordmi Ma'su mori ATTORNEYS PATENTEDUBI 16 I973 Yield(%) sum 02 0F 10 D 650C A550C Colcining time (hr) PATENTFDUBY 15 ms SEMI 03 0510 3 0 92; 3 on 98 L $82 S 29? B wtumv OO Om Om ON Ow On 0% Om cozE mocoo 35 5o; k E258: N00 o 950: m L 2258: N00 x PI M PATENTED URI '1 6 I975 SHEET 0 OF 10 Fig.4

TAL E Portiul pressure of CO2 (01m) PATENTEU BC! 16 I973 sum 0SUF10 Fig.5

OQ O0 Temperature (C) PATENIEDucr 16 1975 SHEET 08 0F 10 Method of invention :3: irrocnkel X Known meihod g3; Rigid Reducing 1emperoture(C) PATENTEUnm 16 ms 3.765.873

sum 07 or 10 Fig.7

Target-Co Pmmmum 181975 3.765873 sum 08 or 10 F Fuyolite I Q cL-Q: d- Quartz W: Wusfite Target Co PATENIEUnm m 1915 SHEU 09 0F 10 Qo vcozoaug 6 0 m 1 0 fcr Ni Method of mvenhon (I CPHO for Fe Melhod of invention (2) x for -X for Known method K h d 2) for N; nown me! e fw Fe Reducing temperoiure (C) PATENTEUUET 16 ms 3765873 sum 10 or 1o F F Fe-Ni F: Foyolite Forsterite Target-Co This invention relates to a method of producing ferro-nickel or metallic nickel, and more particularly to a method of producing ferro-nickel or metallic nickel from iron-rich nickel ore or iron-rich nickel oxide. The present invention also relates to a method for producing ferro-nickel or metallic nickel from nickel ore and nickel oxide containing a large amount of iron, by adding separately prepared silica to the starting material, which silica is prepared, for instance, by removing magnesia from nickel magnesium silicate ore.

Nickel is an indispensable metal for making stainless steel and heat-resisting alloy. As the consumption of nickel increases, the availability of high grade nickel ores gradually decrease, and there has been an increasing need for a process of making ni'ckel from comparatively low grade ores, such as laterite, containing a large amount of iron, as shown in Table 1. There have been a number of studies made heretofore on the process of producing ferronickel from iron-rich nickel ore. Among such studies, the nickel-preferred reduction is most important.

What is meant by the nickel-preferred reduction is based on the difference in the thermodynamic properties of nickel and iron; namely, iron has a greater affinity for oxygen than has nickel. In an actual refining process for the reduction of iron-rich nickel ore, such as laterite, however, iron and nickel are simultaneously reduced, and it is very difficult to give preference to the reduction of nickel over that of iron. More particularly, when iron-rich nickel ore is reduced in a conditioned gaseous atmosphere, both nickel and iron are simultaneously formed by reduction, and the resultant ferronickel has a comparatively low nickel content. It has been difficult to improve the nickel content in the ferro-nickel by any further treatment.

The inventors have noticed the fact that iron contained in iron-rich nickel ores can be fixed in the form of difficultly reducible fayalite, so that the selective reduction of nickel can be effected based on the difference of the reducibility between fayalite and nickel compound.

The formation and decomposition of fayalite (2FeO 8102) can be represented by the following chemical formulae.

2Fe O -l-. 3Si0 2C0 3(2Fe0 SiO 2C0 ZFeO sio2 2C0 2Fe sio2 2C02 lic nickel from iron-rich nickel ores by adding silica so 2 as to positively use the formation of lective reduction of nickel.

TABLE 1 Chemical composition (percent) F0 CaO MgO A12 03 01'0 SiOz Ni CrzOa Garnierite 7 However, most silica-rich nickel ores contain a larger amount of magnesia, for instance, 20-30% of magnesia in the case of garnierite, as shown in Table l. The chemical behavior of such magnesia in the nickel ore during any wet nickel refining process is similar to that of nickel oxide. Accordingly, the presence of magnesia is detrimental to the wet nickel refining process. It is also known that the presence of a large amount of magnesia is not desirable in dry nickel refining processes, such as the Krupp-Renns process. After years of study, the inventors have succeeded in developing an improved nickel refining process from both iron-rich nickel ore (e.g., laterite) and nickel magnesium silicate ore (e.g., garnierite), in which magnesia in the nickel magnesium silicate ore is extracted by using carbon dioxide gas, and the residue from the magnesia extraction is used as the silica source for the formation of fayalite in the refining process of the iron-rich nickel ore. The nickel refining method of the present invention has the following advantages.

1 Ferro-riickel or metallic nickel of high grade can be achieved, because reduction is accelerated for both nickel in iron-rich nickel ore and nickel in the residue from magnesia separation of nickel magnesium silicate ore.

i 2 The carbon dioxide in the exhaust g a s from the re duction of both iron-rich nickel ore and the residue from the magnesia separation of nickel magnesium silicate ore can be used for the extraction of magnesia from the nickel magnesium silicate ore, so that the overall heat efficiency of the process is improved.

Thus, another object of the present invention is to provide an improved nickel refining method comprising two groups of steps; namely, a group of steps for pretreating the nickel magnesium silicate ore for extracting magnesia, and another group of steps for producing ferronickel from the iron-rich nickel ore by using the residue from the first group of steps.

It is one of the important features of the present invention that conventionally discarded magnesium in the nickel magnesium silicate ore, such as garnierite, is extracted in the form of magnesia for useful applications. Since the magnesia thus extracted has certain commercial value, the overall economy of the nickel refining process from iron-rich nickel ore can considerfayalite for the seably be improved, in which the residue from the magnesia extraction can be used as the silica source for the formation of fayalite from the iron compounds contained in the iron-rich ore, which fayalite is effective in suppressing the reduction of iron compund.

For a better understanding of the invention, reference is made to the accompanying drawings, in which:

FIG. 1 is a flow diagram of an embodiment of a nickel refining process according to the present invention;

FIG. 2 is a graph showing the relation between the yield of magnesia and calcining conditions;

FIG. 3 is a graph, showing the relation between the yieldof magnesia and the concentration of calcined ore in the slurry;

FIG. 4 is a graph, illustrating the relation between the yield of magnesia and the partial pressure of carbon dioxide in the gas blown into the slurry of calcined nickel magnesium silicate ore;

FIG. 5 is an equilibrium diagram for reducing reactions in an Fe-SiO-C-O system;

FIG. 6 is a graph, illustrating the relation between the degree of reduction and temperature in the reducing process, according to the present invention;

FIG. 7 is an X-ray diffraction diagram of typical fayalite;

FIG. 8 is an X-ray diffraction diagram of products from an embodiment of the present invention;

7 FIG. 9 is a graph, illustrating the relations between the degree of reduction of nickel and iron and the reducing temperature; and

FIG. 10 is an X-ray diffraction diagram of products formed in a different embodiment of the present invention.

The principles of the present invention will be described, referring to an equilibrium diagram of reducing reactions in an Fe-SiO -C-O system, or an iron ore reducing system, as shown in FIG. 5. Laterite and garnierite contain iron in the form of limonite (Fe O 1111 0 The limonite releases its Water of crystallization at about 300 to 350 C and becomes ferric oxide Fe O The ferric oxide Fe O can easily be reduced by carbon monoxide to produce Fe O, according to the following chemical reaction. The concentration of carbon monoxide in the gas for the last mentioned reduction can be low.

31%,0, co zre o, co,

The minimum content of carbon monoxide in the reducing atmosphere for the production of fayalite is at least 1.6% at 400 to 1,400 C, and fayalite can easily be formed without regulating the reducing atmosphere.

If, however, there is no silica available for the reducing reaction (4), Fe O generated by the reduction (3) is further reduced to FeO or Fe, as shown by the line C-C D in FIG. 5, and Fe() is further reduced to metallic iron, as shown by the line C'-E of FIG. 5.

On the other hand, fayalite (Z FeO SiO which can be formed by the presence of silica and a comparatively low content of carbon monoxide, cannot be reduced unless the content of carbon monoxide in the reducing atmosphere is much higher than that required for the reduction of simple iron oxide. More particularly, the reducing of fayalite to metallic iron takes place only when the content of carbon monoxide in the reducing atmosphere is or higher, as shown by the line F-F of FIG. 5.

Accordingly, in treating iron-rich ore and iron-rich nickel oxide, such as laterite, it is possible to suppress the reduction of iron oxide in a reducing atmosphere by adding silica. In other words, silica can be used as a kind of fixer for stabilizing iron in the reducing atmosphere.

It is an important feature of the present invention to form fayalite intentionally by adding silica. In fact, the formation of fayalite has heretofore been avoided in the art of iron manufacture. Contrary to such conventional practice in iron manufacturing industries, the present invention intends to take advantage of the fa yalite formation for accelerating the nickel reduction while suppressing the iron reduction.

Due care should be given to the chemical behavior of nickel in the presence of silica in a reducing atmosphere. A compound of nickel oxide and silica has been known, which is referred to as nickel olivine (2NiO cess according to the present invention, the presence of silica will become detrimental to the nickel refining, because nickel olivine is hardly reducible.

The inventors have confirmed that the method of the invention is free from such formation of nickel olivine. In fact, tests were made by adding silica and silicacontaining residue, to be referred to hereinafter, in laterite ore from New Caledonia. The mixture of the ore and silica thus added was reduced by heating it at 600 to 1,200 C. It was found by such tests that the silica thus added was effective in suppressing the reduction of iron but not the reduction of nickel. The reduction of nickel was actually improved in the case of using the silica-containing residue by the presence of the silica.

The freedom of the method of the present invention from formation of nickel olivine seems to be in the fact that, in the case of iron-rich nickel ores, such as laterite, metallic nickel being reduced tends to melt in metallic iron, and the activity of the nickel in the reducing system is so reduced that nickel olivine is not formed despite the presence of silica. When the silicacontaining residue made from nickel magnesium silicate ore is used, the crystal structure of the residue is broken by the formation of fayalite, so as to accelerate the reduction of nickel.

The chemical composition of laterite ores varies, depending on where they are produced. Typical composition of lateritescurrently available in Japan is shown in ing atmosphere are greatly simplified, and various kinds of reducing agents in solid, liquid, and gas phase can be used, such as coke, coal, natural coke, hydrocarbon gas, carbon monoxide gas, etc.

The content of carbon monoxide in the reducing atmosphere, which is necessary for the reduction of nickel according to the present invention, should be within the range above the line B-B" of FIG. 5. Theoretically, such range of carbon monoxide content (B-B") is below the lower limit of carbon monoxide for fayalite formation in the reducing atmosphere (B-B), and there is no difficulty in preparing it. The silica to be used in the method of the invention for fixing iron in the laterite can be either pure silica or silicacontaining ores. Natural silica and mountain sand are most commonly used for such purposes.

The silicate ores to be used as the source of silica in the method according to the present invention, for fixing iron, may sometimes contain magnesia (MgO). This magnesia reacts with SiO to form forsterite, which is a substituted compound similar to fayalite. The forsterite thus generated may form a solid solution together with fayalite, which is known as forsterite-fayalite. Accordingly, if magnesia is present in the silica source, fayalite may not be generated as a simple compound, but it often takes the form of a solid solution of forsteritefayalite. Thus, the iron compound to be formed in the method of the present invention for controlling the reduction of iron is not restricted to fayalite alone, but it may include solid solutions of fayalite with other compounds, such as forsterite-fayalite solid solution.

In the foregoing description, laterite is used as the iron-rich nickel ore for producing ferro-nickel or metallic nickel according to the present invention. The starting material of the method of the present invention, however, is not restricted to laterite alone, but any other iron-rich nickel ores may be used, such as garnierite and iron enriched gamierite. Furthermore, any nickel oxides with high iron-content may also be used as the starting material of the method of the invention, even when such compounds are not in the form of ore.

As pointed out in the foregoing, one of the important features of the present invention is in the use of nickel magnesium silicate ore, e.g., gamierite, as the silica source after separating magnesia therefrom. Such process will now be described in detail, referring to the flow diagram of FIG. 1. The ore to be used as the silica source, such as garnierite, is at first crushed to the grain size suitable for the next following step of calcination,

which gram size 1s usually about 100 mesh or finer.

The ore thus crushed is calcined at about 500 to 800 C, to remove the water of crystallization in the ore, for separating gangue component (MgO) by decomposing the crystal structure of magnesium silicate. A slurry was made by adding eight to 50 parts by weight of water to one part by weight of the ore thus calcined. The slurry is agitated in a slurry tank at 20 to 50 C for about 0.5 to 3 hours, by blowing carbon dioxide gas (G0,) at different pressures in the range of l to about 20 atmospheric pressures. Thereby the magnesia in the calcined ore reacts according to the following chemical reaction, so as to dissolve magnesium thus isolated.

The slurry thus agitated is filtered at an elevated pressure. The filtrate is suddenly exposed to the atmospheric pressure or boiled, so as to generate precipitates of magnesium carbonate MgCO 3H O, while causing evaporation of carbon dioxide gas dissolved therein.

The operating conditions of the aforesaid separation of magnesia from starting nickel magnesium silicate ore will now be described in further detail. The starting ore is crushed, preferably to the grain size of mesh, as pointed out in the foregoing, so as to facilitate the succeeding calcining and extracting processes.

The purpose of the calcining process is to thermally decompose the ore, so as to prepare it for the separation of magnesia MgO. In the ore, both magnesia MgO and nickel oxide are in the form of solid solution with silicate, and by the calcination, the magnesia MgO is converted into an easily extractible form and nickel is converted into an easily reducible form. The temperature for initiating the decomposition of the crystal of the nickel magnesium silicate ore, which crystal contains MgO in the form of hydrous silicate, is about 500 C, preferably 600 C. Thus, the minimum temperature for the calcination is 500 C. Magnesia MgO and silica SiO thus separated from the crystal of the nickel magnesium silicate ore by the calcination may be recombined to form hardly separable forsterite (2Mg0 -SiO if tlTey are heated to 800 C or higher. Accordingly, the calcining temperature should be below 800 C. Therefore, the suitable range of calcining temperature is 500 to 800 C.

FIG. 2 shows the relation between the yield of magnesia and one of the calcining conditions, i.e., calcining time. The yield is expressed in terms of the percentage of the amount of MgO extracted in the form of MgCO 83H O to the amount of MgO originally contained in the starting ore. Namely,

Yield Amount of MgO extracted/Amount of MgO originally present in the ore X 100% The configurations of FIG. 2 were determined by measuring the yield for different durations of calcination, while keeping other conditions constant, such as the slurry concentration and the partial pressure of carbon dioxide gas. The ordinate represents the yield, and

the abscissa represents the calcining time.

It is apparent from FIG. 2 that when the duration of calcination is about 1 hour, more than 30% of MgO yield can be achieved provided that the calcining temperature is in the range of 600 to 700 C. The highest yield can be achieved by effecting the calcination for 2 to 3 hours at 600 C.

Water is added to the ore thus calcined, to prepare a slurry. The concentration of the ore in the slurry should preferably be low, because the solubility of the magnesium bicarbonate, to be generated in the next step, is about 0.64 gram/100 cc H O at 35 C under the atmospheric pressure. In order to determine the industrially useful range of the slurry concentration, tests were made by determining the yield of magnesia for different concentrations of the calcined ore in the slurry. The quantity of water in the slurry was varied from one to 40 parts by weight per one part by weight of the calcined ore. Carbon dioxide (CO gas treatment was carried out for one hour by blowing a gaseous mixture of CO and N,, with 20% of C0,, into the slurry, at a rate of 2 liters/minute, while keeping the reaction temperature at 35 C and exposing the slurry to atmospheric pressure. The results are represented by the curve P-P' of FIG. 3. In FIG. 3, the ordinate shows the yield of magnesia, as defined in the foregoing, reference to FIG. 2.

It is apparent from the curve P-P' of FIG. 3 that the yield of magnesia is larger than 30%, if more than eight parts by weight of water is added to one part by weight of the ore. To check the effects of more dilute slurry, different slurry samples were prepared by adding eight to 100 parts by weight of water in one part by weight of the ore, respectively. The yield of magnesia was determined by treating each of the slurry samples for 3 hours by blowing a C gas, at a rate of 2 liters per minute, while keeping the reaction temperature at 35 C and the reaction pressure at Kglcm The results are represented by the curve Q-Q' of FIG. 3.

Judging from the curves P-P and 0-0 of FIG. 3, the suitable concentration of the calcined ore in the slurry is eight to 50 parts by weight of water per one part by weight of the ore, based on reasonable duration of the carbon dioxide treatment, such as l to 3 hours. If the quantity of water is less than eight parts by weight per one part by weight of the ore, the yield of magnesia is too low, while if the quantity of water exceeds 50 parts by weight per one part by weight of the ore, the yield cannot be improved although the facilities must be expanded for handling the increased quantity of water.

The slurry of the calcined ore is subjected to carbon dioxide treatment in a slurry tank by blowing a carbon-dioxide-containing gas thereto, so as to effect chemical reaction (5). In this carbon dioxide treatment, if the reaction temperature is too low, the reaction velocity becomes too slow. On the other hand, if the reaction temperature is too high, the solubility of carbon dioxide gas is undesirably lowered. For reasonable durations of the carbon dioxide gas treatment and treating pressures, for instance, in the case of one hour treatment at the atmospheric pressure, the preferred temperature range is 20 to 50 C.

The pressure of carbon dioxide gas, or the partial pressure of C0 in the carbon-dioxide-containing gas, should be determined by considering the solubility of carbon dioxide gas in water. Generally speaking, high partial pressure of CO is effective in improving its solubility in water and improving the yield of magnesia MgO. The effects of the partial pressure of CO, on the yield of magnesia was checked by blowing carbon-dioxide-containing gas with different partial pressures of CO, in a slurry for l hour at 50 C. The slurry was made by adding parts by weight of water to one part by weight of the calcined ore. The partial pressure of CO was varied in the range of l to 7 atm. The results are shown in FIG. 4.

It is apparent from the figure that the yield of magnesia increases rapidly when the partial pressure of CO is raised from 1 atm. to about 2 atm. For the partial pressure higher than about 2 atm., the improvement of the yield in response to the raising of the partial pressure is slowed down.

In filtering the slurry thus treated, it should be noted that both the slurry before filtering and the filtrate should be kept at the same pressure level, because if the pressure of the slurry is reduced before the filtering, the magnesium ions dissolved in it at high pressure may crystallize in the form of MgCO Ill-I 0, as pointed out in the foregoing. Accordingly, in the actual slurry tank by Examples. Example 1:

for effecting the carbon dioxide treatment, a partition means is provided to define a filtrate chamber, which is contiguous to a slurry chamber holding the slurry. The filtering process may be carried out while keeping both the slurry chamber and the filtrate chamber at the same pressure level. Therefore, the reduction of pressure of both filtrate chamber and slurry chamber may be followed after ending of filtration.

The content of silica in the residue thus prepared is considerably improved, as compared with that in the starting ore. For instance, some of the garnierite ores, which were used in one of the tests made by the inventors, contained 40.62% of SiO and 2.97% of (NH-Co), and such contents were improved to 49.45% and 3.75%, respectively, by the aforesaid magnesiumremoving treatment. Thus, excellent sources of silica are prepared, which can also be used as the source of nickel. Besides, the reducibility of nickel is greatly improved by decomposing the hydrous silicate crystals through the aforesaid calcining process.

The filtrate contains Mg, and as the pressure of the filtrate is changed, for instance, by exposing it to the atmosphere or by boiling it, the residual carbon dioxide gas is expelled from the filtrate to product precipitates of MgCo 3H O. One can recover magnesia from such precipitates. I

The residue thus prepared (to be referred to as silica-containing residue, hereinafter), by removing magnesia from the nickel magnesium silicate ore, is then mixed with iron-rich nickel ore or iron-rich nickel oxide. The mixture is heated in a reducing atmosphere at a temperature high enough for generating fayalite or fayalite-forsterite solidv solution, so that the reduction of nickel may be accelerated while suppressing the reduction of iron by means of the fayalite or fayaliteforsterite solid solution thus generated.

The silica-containing residue includes a sizable amount of nickel, in addition to the silica, and hence, the residue can be used both as a silica source and a nickel source.

As a result of the aforesaid reducing treatment of the iron-rich nickel ore or iron-rich nickel oxide, by using the silica-containing residue, there is produced 'luppe (puddled iron) containing reduced nickel. The desired ferronickel with a high nickel content can be obtained by crushing, and removing the fayalite or the fayaliteforsterite solid solution by a table type or wet type magnetic separator. In the magnetic separator, the iron component in the form of fayalite or fayalite-forsterite solid solution is transferred to slags, due to the nonmagnetic properties of such form of the compound.

According to an important feature of the present invention, the exhaust gas from the reducing process of the mixture contains hot carbon dioxide gas, and such exhaust gas can advantageously be used for the separation of magnesia from the slurry of the nickel magnesium silicate ore, as shown in FIG. 1. Thereby, the overall heat efficiency of the nickel refining process according to the present invention can be kept at a high level. It is also possible to use the hot exhaust gas from the reducing process for heating the nickel magnesium silicate ore to be calcined for the separation of magnesia. Thereby, the overall heat efficiency will further be improved. I

The invention will now be described in further detail Nickel magnesium silicate ore consisting of garnierite from New Caledonia, which has a chemical composition as shown in Table 2, was crushed to a grain size finer than 100 mesh and calcined at 600 C for 2 hours.

The formation of fayalite was confirmed by using X-ray diffraction diagrams. For this purpose, an X-ray diffraction diagram of standard fayalite was separately prepared, and the X-ray diffraction diagram of the ac- A slurry was made by adding 200 cc of water in grams 5 tual samples were compared with the standard diagram of the ore thus calcined, and then agitated for 2 hours for checking the formation and the presence of fayalite. while blowing the exhaust gas from the reducing pro- The samples treated by the method of the present incess, to be described hereinafter, at a rate of 1 literlvention and the conventional method were analysed, min, for dissolving carbon dioxide gas therein. The exand the results are shown in Table 4. The degree of rehaust gas was 40 C and consisted of about of car l0 duction R, as defined above, was determined for each bon dioxide gas, and about 80% of nitrogen gas, incluof the samples thus treated, and the results are shown sive of about 0.1% of carbon monoxide gas. The agitain FIG. 6. I tion was carried out at the atmospheric pressure, and ltis apparent from Table 4 and FIG. 6 that, with the the slurry thus agitated was then filtered at the atmoconventional method, the iron oxides and nickel oxides spheric pressure. The filtrate was boiled to precipitate 15 of the ore are simultaneously reduced to produce memagnesia (MgO) in the form of magnesium carbonate. tallic iron and metallic nickel. Especially, when the ore The yield of the magnesia proved to be 33%. is treated at l,200 C by the conventional method,

TABLE 2 Composition Ignition Ore loss SiOz F6203 A1103 CaO MgO N1+Co Garnierite from New Caledonia 10. 72 40. 62 15. 54 0.60 0. 24 27. 34 2. 97

7 Example 2:

there are no Fe and Fe ions left in the final products, so that most of the iron contained in the starting ore is reduced to metallic iron. On the other hand, with the method of the present invention, iron oxides in the starting ore are hardly reduced, while nickel oxides therein are reduced at an increased rate.

Table 5 shows the content of metallic nickel in the metallic products of Table 4, which is'defined as follows.

(metallic nickel)/(metallic nickel) (metallic iron) TABLE 4 Treating Composition (percent) temperature Total Metallic Total Metalhc Treating method C.) iron iron Fe++ Fe nickel nickel Method of the 800 51. 33 2. 97 47. 88 0. 4s 1. 31 0. invention 1, 000 52.00 6. 57 42. 94 2. 49 1. 33 V 1. 09 1,200 53. 62 10.28 43. 11 0. 23 1. 41 '1. 31 Conventional 800 63. 21 25. 21 29. 13 8. s7 1. 87 1. 11 method 1, 000 70.35 58. 72 9. 52 2. 11 2. 04 1.88 1, 200 '72. 40 68.35 3. 92 0. 13 2. 07 2. 02

, TABLE 3 TABLE 5 f Composition I Ir 111 IV Ignition Metallic Ore loss Fe Ni S102 A120: CaO MgO iron plus Content of Treating metallic metallic Laterite trom temper- Metallic Mejiaulc nickel nickel, New Cale- 1 Treating atuxe iron, mcke (1+ 11) II/IlIXlOO, donia 11.68 50. 45 1.41 3.18 4.48 0.43 1. 28. thod O percent percent (percent) percent A ii of 97 0 45 a 42 1a 27 t einven- 800 2. For mak ng acomparrson, the ir on I'lCh nickel ore tion 1,000 6.57 1'09 M6 M20 having a chemical composition of Table 3 wa-reduced C to 1, 2 g ga a 13;. onven l n- 1n the same manner as described above, but without 1,000 5&72 L88 6M0 L79 adding any silica therein; namely, the same reducing 1,200 -35 70- 7 2.88

conditions, inclusive of temperature, carbon monoxide concentration, and reducing time, were used in the same test furnace for the latter test reduction.

In these tests, the following degree of reduction R was determined for each of the samples, which were treated at different temperatures.

(Decrease in the amount of oxygen by the reduction) (Amount of oxygen'combined With-iron or nickel before the reduction) The above degree of reduction R corresponds to the commonly used deoxidation ratio.

As can be seen from Table 5, the content of nickel in the metallic product made by the method of the present invention is more than 10%, while the correspond- ;ing content in the metallic product of the conventional imethod is low. For instance, if the starting material'is be used for the manufacture of high grade ferronickel. The mixture of the iron-rich nickel ore and the silica- For instance, laterite can be used as the starting matecontaining residue thus prepared contained magnesia, rial of nickel making, according to the present inven- .as shown in Table 7, and the magnesia forms forsterite tion. (2Mg0 SiO during the reducing process, as pointed As a reference for checking the formation of fayalite, out in the foregoing. This forsterite reacts with fayalite an X-ray diffraction diagram of standard fayalite was and forms fayalite-forsterite solid solution. Accordtaken, as shown in FIG. 7. Similarly, another X-ray difingly, not all the silica in the mixture, as shown in Table fraction diagram was taken for the sample being 7. is available for the formation of Fayalite. it is calcutreated at 1,000C according to the present invention, lated that only 15.07% of the silica, based on the total as shown in FIG. 8. In comparing FIGS. 7 and 8, it is mixture, is available for the formation of fayalite, and

apparent that fayalitewas formed by the method of the about 27% of iron, based on the total mixture, can be present invention, for suppressing the reduction of fixed by such silica. iron.

. ,l The mixture was reduced at different temperatures, Exafnple 31 v i.e., 600, 800, 1,000, 1,200", and l,300 c, for 1.5 Nickel magnesium silicate ore with the composition hours respectively Th6 reducing process was carried of Table 2 was crusbed to a grain Size finer f' out in a testfurnace by adding 5% of coke as a reducing mesh, and then calcined at 600 C for 2 hours, lll the agent, while blowing argon gas therethmugh same manner as Example 1. A slurry was made by add-,

ing 40 parts by weight of water to one pal. by weight For the sake of comparison, similar reducing process of the ore thus calcined. The slurry thus prepared was was camed out by uslflg P carbon momfxlde g agitated for 1 hour by blowing the exhaust gas from the the Coke F E as 3 5 reducmg agent in reducing process to be described hereinafter, at a pres: case the reducmg was also sure of 10 Kg/cm (gauge pressure). The slurry thus ag- For further comparison, the iron-rich nickel ore with itated was filtered by using a filter cloth, while keeping the composition of Table 3 and the silica-containing the slurry tank at 10 Kg/crn and the filtrate chamber residue with the composition of Table 6 were separessure at 8.5 to 9 K lcm ratel reduced without mixin to ether. The conditions P g y g g The yield of Mg() in this process was about 43%, and of the reducing process were the same as those for the the yield of Ni() was 2.4%. The chemical composition reduction of the mixture, and both coke and pure car- Of the silica-containing residue was determined, as bon monoxide gas were used as the reducing agent for shown in Table 6. the separate reducing processes of the iron-rich nickel TABLE 6 Composition (percent) Ignition Material loss SiO Feet); Aid); 0210' .\lg0 Ni-i-Co Siliea-containing residue 5. 64 49.45 18.95 I 0. 7-1 0.30 19. it) 3.57

A- mixture was made by adding 140 parts by weight ore and the silica-containingresidue, respectively. of iron-rich nickel ore (laterite from New Caledonia), The results are shownin Table 8, and the relation with the composition of Table 3, into 100 parts by between the reducing temperature and the degree of weight of the silica-containing residue with the comporeduction i ho i FIG 9, sition of Table 6. Thecomposition of the mixture thus The reducing process (1) of the present invention in prepared was determined as Shown in Tab e 7 Table 8 uses coke and argon at'mosphere for constitut- TABLE? 7 Composition (percent) Iron, 'Niekel, Silica, Magnesia, Calcium Alumina, ignition Material ,Fe Ni SiOg I MgO oxide, CaO A1201 loss Mixture of iron-rich ore and Silica-containing residue 35.66 2.19 21.22 8.25 Trace 2. 97 8.58

TABLES ing the reducing atmosphere, while the reducing pro- Reducing Metallic Metallic cess (2) of the present invention in Table 8 uses pure temperairon, nickel, sample tumors percent percent carbon monox de gas for such purposes. The equilib 600 0 16 0 07 j rrum diagram of FIG. 5 does not show such gaseous at- Method oithe. Mixture otthe ore 800 o. 18 L 0104. mosphere for the reduction. Such reducing gases were mvenno 3 f Fggg 33% g- 2% g used, because the materials beingreduced in the actual 11300 14.35 2. 61 Examples were not pure compounds, while the equilibfiflfi 109 rium diagram of FIG. 5 is based on pure compounds, Method of the Mixture of the ore 800 16. 3t 0. 55 invention (2) andthe Hm 11600 23.31 1&0 and the gap between the actual complicated corn du 38 i2 8; 3-22 pounds and the pure compounds assumed in FIG. 5 should somehow be'filled. In addition, the use of argon 2% 8%; 3: Z atmosphere makes up for the instability of carbon mon- Know method 2,,,,,;;;g?; p :3 oxide gas and the consumption of the carbon monoxide 1:300 714;; 5 gas by the reducing reactions. 4 6m, 5 58 u 42 5 In this Example, comparatively strongly reductive ath d 2 The ga -rich mosphere was actually used, due to the last mentioned Known met 0 li :04 1 reasons. The formation of fayalite is not disturbed by such strong reducing nature of the atmosphere, be-

1 Reducing agent-coke (argon p cause a wide range of reducing gas concentration is al- 2 Reducing agent-Pure 00 gas.

lowed for the formation of fayalite, as pointed out in the foregoing.

If the reducing temperature is higher than l,400 C, fayalite may be reduced by solid carbon as in the case of a blast furnace for pig iron. Thus, for the reduction at 1,400 C or higher, the amount of carbon to be added must be limited to the bare minimum, which is necessary for the reduction of iron and nickel.

It is apparent from Table 8 and FIG. 9 that the degree of reduction of iron and the amount of metallic iron in the reducing process of the present invention are reduced as compared with those of the known method (2). The difference in the amount of metallic iron increases when the reducing temperature exceeded l,000 C, at which the formation of fayalite and fayalite-forsterite solid solution begins. Such difference in the amount of metallic iron indicates the effectiveness of the presence of fayalite for suppression of the reduction of iron, or for fixation of iron. In other words, the reduction of iron can be controlled by the use of fayalite. In fact, the control of iron reduction by fayalite is more reliable and accurate than by mere regulation of the reducing atmosphere.

As regards the reduction of nickel, it is apparent from the comparison of the methods (I), (2) of the present I invention with the known methods (1), (2) that the nickel reduction is not affected by the presence of fayalite and fayalite-forsterite solid solution. Furthermore, the rate of metallic nickel'productionin the method of the invention is superior to that of the known method (1), even at an elevated temperature. This improvement in the degree of nickel reduction is due to the fact that the reduced nickel forms a solid solution with metallic iron to reduce its activity, and that the formation of fayalite by using iron contained in the ore accelerates the breakdown of crystalline structure of nickel magnesium silicate ores, e.g., garnierite.

The use of fayalite for the control of iron reduction is not only a feature of the present invention but also the finding of the inventors, on which the present invention is based.

Inspection of the sample metal prepared by the method of the present invention indicated that nickel was in the form of very fine particles, of diameter of about one micron. Such fact means that the addition of silica in iron-rich nickel ore, such as laterite, was highly effective in the production of fine metallic nickel particles.

In FIG. 9, it is noticed that the degree of reduction of iron and nickel in the method (2) of the present invention was lowered at l,300 CfThis decrease in the reduction is due to the fact that the ores being treated was in a semi-molten state, and the permeation of reducing gas was restrained.

An X-ray diffraction diagram was prepared for the sample, which was treated by the method (2) of the present invention at l,200 C. The result is shown in FIG. 10. The comparison of FIG. 10 with FIG. 7 clearly indicates that fayalite and fayalite-forsterite solid solution were generated in the sample being treated by the method of .the present invention.

The effects of the method of the present invention may be summarized as follows.

1. The calcination of nickel magnesium silicate ore at 500 to 800 C results in the separation of water of crystallization in the silicate, so as to break down the crystal structure of magnesium silicate. As a result, magnesia is separated, and nickel is activated, sothat magnesia can easily be removed and the yield of metallic nickel in the next succeeding step can be improved.

2. The carbon dioxide gas treatment and filtration of the slurry made by adding water in the calcined ores results in the separation of magnesia and silica-containing residue. As a result, all the components of garnierite ores, inclusive of magnesia, silicate, and nickel, can be fully utilized.

3. The reduction of nickel while suppressing the iron reduction, according to the present invention, is established in that iron-rich nickel oxide or ironrich nickel ore is mixed with silica-containing residue after the removal of magnesia from nickel magnesium silicate ore, and that the mixture is heated at a temperature high enough for the formation of fayalite in an atmosphere containing carbon monoxide and carbon dioxide under the conditions of (CO/CO+CO being 1.6 to so that the formation of fayalite may be used for the suppression of iron reduction. Consequently, the following features can be achieved.

a. Iron-rich low grade nickel ore can be used for producing high grade ferro-nickel ore metallic nickel at a high yield.

b. Reducing atmosphere of wide composition range can be used, in solid, liquid, or gas phase. Thus,

t he operation is easy..

c. The silica-containing residue from the separation of magnesia from nickel magnesium silicate ore usually contains nickel, and the addition of such silica-containing residue in iron-rich ore or ironrich nickel oxide results in the increase in the absolute amount of nickel available for nickel reduction, as compared with the corresponding amount when pure silica is added instead of the residue.

4. The exhaust gas from the nickel reducing process can be used for the separation of magnesia in the slurry. The overall heat efficiency is improved, resulting in a reduced cost of magnesia.

5. The exhaust gas from the nickel reducing step can also be fed back for the calcination step in the flow sheet of FIG. 1 as shown in dotted line, whereby the overall heat efficiency of the process is considerably improved.

What is claimed is:

l. A method of refining nickel by reducing iron-rich starting material and nickel magnesium silicate ore comprising 7 crushing the nickel magnesium silicate ore;

calcining the nickel magnesium silicate ore thus crushed at 500 to 800 C; adding water to the nickel magnesium silicate ore thus calcined to make a slurry; v agitating the slurry by blowing a carbon dioxidecontaining gas therein, the gas having a partial pressure of carbon dioxide gas of not lower than one atmospheric pressure; filtering the slurry so as to produce a magnesia-rich filtrate and a silica-containing residue;

extracting magnesia from the filtrate by precipitating magnesium carbonate and decomposing the magnesium carbonate into magnesia and carbon dioxide gas;

mixing the silica-containing residue with the iron-ric h starting material; and

heating the mixture in a reducing atmosphere containing carbon monoxide and carbon dioxide wherein the ratio CO/CO-i-CO is .016 to .90 at a temperature from 400 to l,400 C for producing fayalite or a fayalite-forsterite solid solution and recovering metallic nickel or ferro-nickel.

2. A process according to claim I wherein the heating step produces an exhaust gas product which contains carbon dioxide and further wherein the exhaust gas product is employed at a total pressure of at least five atmospheres and a carbon dioxide pressure of at least one atmosphere as the carbon dioxide gas in the agitating step.

3. The method according to claim 2, wherein said iron-rich starting material is laterite and said nickel magnesium silicate ore is garni erite.

4. The method according to claim 1, wherein said nickel magnesium silicate ore is crushed to a grain size finer than mesh.

5. The method according to claim 1, wherein aid slurry is made by adding eight to 50 parts by weight of silica-containing residue as a reducing agent. 

2. A process according to claim 1 wherein the heating step produces an exhaust gas product which contains carbon dioxide and further wherein the exhaust gas product is employed at a total pressure of at least five atmospheres and a carbon dioxide pressure of at least one atmosphere as the carbon dioxide gas in the agitating step.
 3. The method according to claim 2, wherein said iron-rich starting material is laterite and said nickel magnesium silicate ore is garnierite.
 4. The method according to claim 1, wherein said nickel magnesium silicate ore is crushed to a grain size finer than 100 mesh.
 5. The method according to claim 1, wherein aid slurry is made by adding eight to 50 parts by weight of water in one part by weight of the calcined ore.
 6. The method according to claim 1, wherein the agitation and filtration are carried out with the carbon-dioxide-containing gas under pressure, and the filtrate is exposed to the atmospheric pressure for the precipitation of magnesium carbonate.
 7. The method according to claim 1, wherein said filtrate is boiled for the precipitation of magnesium carbonate.
 8. The method according to claim 1, wherein coke is added to the mixture of the iron-rich nickel ore and the silica-containing residue as a reducing agent. 